1. Field of the Invention
The present invention relates to an organic electroluminescent display, and more particularly, the present invention relates to an organic electroluminescent display having an improved sealing structure.
2. Description of the Related Art
In general, Organic Electroluminescent Displays (OELDs) are self-luminous displays operating at a low voltage by electrically exciting a fluorescent organic compound to emit light. Since OELDs can be made thin, have a wide viewing angle, and have a rapid response rate, they are receiving great attention as a next generation display, eliminating problems arising with liquid crystal displays.
Such an organic electroluminescent display is manufactured by forming an organic layer in a predetermined pattern on a transparent insulating substrate, such as glass, and then forming electrode layers on the top and bottom surfaces thereof. In this organic electroluminescent display, holes injected from anodes migrate toward an emissive layer when an anode voltage is applied to the anode, and electrons injected from cathodes migrate toward the emissive layer when a cathode voltage is applied to the cathode, so that the holes and electrons recombine in the emissive layer to generate exitons. As these exitons transit from an exited state to a base state, luminescent molecules in the emissive layer emit light, thereby forming images.
Organic electroluminescent displays deteriorate as moisture intrudes thereinto, so that a sealing structure for preventing intrusion of moisture is required.
Conventionally, a sealing structure has been used which consists of a metal can or glass substrate formed into a cap having grooves filled with a desiccant powder. In addition, a film type desiccant has been attached using double-sided tape. The use of a desiccant powder complicates manufacturing processes, raises material and manufacturing costs, and increases the thickness of the substrate. Furthermore, due to the area filled with the desiccant powder, front emission or double-side emission, particularly when used together with a non-transparent substrate, cannot be achieved. The film type desiccant is not a perfect sealing structure preventing intrusion of moisture and is liable to be damaged in the manufacture or when used due to its poor durability and reliability. Therefore, the film type desiccant is not suitable for use on a mass scale.
U.S. Pat. No. 5,882,761 relates to an organic electroluminescent display apparatus including a stack of pairs of opposing electrodes with an emissive layer made of an organic compound therebetween, a container sealing the stack from external air, and a desiccant placed inside the container, wherein the desiccant remains in a solid state even after absorbing moisture. This patent suggests the use of an alkali metal oxide, sulfate, etc. as the desiccant. However, the organic electroluminescent display is thick due to the container. Furthermore, the desiccant becomes opaque, although it remains as a solid, after absorbing moisture, so that it cannot be applied to front emission and double-side emission displays. As described above, the manufacture of the organic electroluminescent display apparatus is complicated, and the material and manufacturing costs are high.
Japanese Laid-Open Patent Publication No. 5-335080 relates to a method of forming a protective layer in a thin, organic electroluminescent display including an emissive layer containing at least one kind of organic compound arranged between an anode and a cathode, at least one of which is transparent, the protective layer being made of amorphous silica. In particular, amorphous silica, which has a dense structure, is applied as a thick layer to a second electrode layer to prevent intrusion of moisture from the outside. However, the amorphous silica protective layer cannot absorb moisture present in the electroluminescent display, and accordingly, an additional moisture absorbing material is required.